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Page 1: MOTOR SYSTEM Dr. Zahoor Ali Shaikh. TRANSVERS SECTION OF SPINAL CORD.

MOTOR SYSTEM

Dr. Zahoor Ali Shaikh

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TRANSVERS SECTION OF SPINAL CORD

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MOTOR UNIT

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Types of motor neuron

• α – motor neuron

• γ - motor neuron

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Types of muscle fibers

• Extrafusal muscle fibers ( cause muscle contraction supplied by α - motor neuron)

• Intrafusal muscle fibers or muscle spindle (receptor for stretch reflex, supplied by γ - motor neuron)

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MUSCLE SPINDLE (INTRAFUSAL FIBERS)

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MUSCLE EXTRAFUSAL FIBERS

MUSCLE INTRAFUSAL FIBERS

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Muscle spindle

• Nuclear bag fiber

• Nuclear chain fiber

Sensory innervations of muscle spindle

• Ia – nuclear bag & nuclear chain fibers

• II – nuclear chain fibers

Motor supply – γ motor neuron

Dynamic & Static

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Reflex

• Definition

• Components of reflex arcReceptorAfferent pathwayCenterEfferent pathwayEffector organ

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Components of reflex arc

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Classification of reflexes• Monosynaptic or stretch reflex or tendon jerk

eg. Bicep jerk tricep jerk, supinator jerk

knee jerk, ankle jerk• Polysynaptic reflex

eg. Withdrawal reflex

Abdominal reflex

Plantar reflex• Visceral reflex

eg. Micturation, defecation reflex

Jendressik Phenomenon

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KNEE JERK – MONOSYNAPTIC REFLEX

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POLYSYNAPTIC REFLEX

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WITDRAWEL REFLEX - POLYSYNAPTIC REFLEX

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DIFFERENT REFLEXES SHOWN

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• Motor cortex

• corticospinal (pyramidal tract)

• Upper motor neuron (pyramidal & extrapyramidal tracts)

• Lower motor neuron

• Difference between upper & lower motor neuron lesion (UMNL & LMNL)

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MOTOR TRACTSMOTOR TRACTS

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DIFFERENCE BETWEEN UPPER & LOWER MOTOR NEURON LESION

UMN LESIONUMN LESION

• Paralysis affect movement rather than muscles

• Muscle wasting is only from disuse, therefore slight. Occasionally marked in chronic severe lesions.

• Spasticity of clasp-knife’ type. Muscles hypertonic.

LMN LESIONLMN LESION

• Individual muscle or group of muscles are affected.

• Wasting pronounced.

• Flaccidity. Muscles hypotonic.

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• Tendon reflexes increased. Clonus often present.

• Superficial reflexes diminished or modified.

Abdominal reflex absent.

Babinski’s sign +ve, Increased jaw jerk.

• Tendon reflexes diminished or absent.

• Superficial reflexes often unaltered.